Process for encapsulating articles with optional laser printing

ABSTRACT

Articles, such as electrical circuits or elements, are encapsulated by melting polyarylene sulfide in combination with at least one print compound such as monazo-nickel complex, lead chromate-lead molybdate, quinacridone, Ni-Sb-Ti, Co-Zn-SiO2 or lead chromate, injecting this molten composition around the article to be encapsulated, and cooling and solidifying the molten composition. The articles may latter be laser printed.

This is a divisional application of Ser. No. 429,738, filed Sept. 30,1982, now U.S. Pat. No. 4,443,571.

BACKGROUND OF THE INVENTION

Polyphenylene sulfide is a plastic which, due to its stability at hightemperatures and its resistance against various chemicals, has foundever broadening areas of applications. Among these applications are theuse of polyarylene sulfide as an encapsulating material for electricalcircuits or other electrical elements, particularly in view of theoutstanding electrical properties of polyarylene sulfide.

For these and other applications of polyarylene sulfide, printing of thepolymer surface sometimes constitutes a problem. Specifically, it isdesirable to print characterizing features or codes on such surfaceswhich cannot be readily removed or erased, and to obtain these imprintsin good contrast.

Laser printing is a technique that had been developed for permanentprinting on certain surfaces.

THE INVENTION

It is thus one object of this invention to provide laser printablesurfaces from novel polyarylene sulfide compositions.

Another object of this invention is to provide a composition thatfurnishes a surface which can be printed by exposure to laser beamsresulting in relatively high contrast prints on the surface.

A further object of this invention is to provide a process to print on apolyarylene sulfide surface.

Yet another object of this invention is to provide a process to producean electric element encapsulated in polyarylene sulfide.

These and other objects, advantages, details, features and embodimentsof this invention will become apparent to those skilled in the art fromthe following detailed description of the invention and the appendedclaims.

In accordance with this invention it has now been discovered that thefollowing compounds when added in varying concentrations render thesurfaces of molded polyarylene sulfide compositions laser printable withgood contrast:

1. Monoazo-nickel complex (yellow)

2. Lead chromate-lead molybdate (red)--(PbCrO₄)/PbMoO₄

3. Quinacridone (red)

4. Nickel-antimony-titanium (yellow)--NiSbTi

5. Cobalt-zinc-silica (blue)--CoSiZn

6. Lead chromate (yellow)--PbCrO₄

These compounds are hereinafter also collectively referred to as "printcompounds".

In this invention the surfaces to be laser printed on are preferablypolyarylene sulfide molded articles. As used herein "molded" includesinjection molding, extrusion, pultruded, vacuum formed, cast,blowmolded, rotational molded, etc.

More specifically and in accordance with a first embodiment of thisinvention, a composition is provided which comprises the followingingredients the broad ranges represent the ranges within which thecomposition should be confined in order to obtain good results, thepreferred ranges are preferred because they define a compositionpossessing the physical, chemical and electrical properties best suitedfor its intended encapsulation purposes:

    ______________________________________                                                      Broad Range Preferred Range                                     Ingredient    Parts by Weight                                                                           Parts by Weight                                     ______________________________________                                        Polyarylene sulfide                                                                         100         100                                                 Print compounds                                                                              .9 to 12   3 to 6                                              Filler         140 to 220 160 to 200                                          Coupling agent                                                                              .7 to 6     1.5 to 3                                            Processing aid                                                                              .3 to 3      .7 to 1.4                                          Corrosion inhibitor                                                                          0 to 6     1.4 to 4                                            ______________________________________                                    

The corrosion inhibitor is optional in the composition but may be addedto provide mold and encapsulated component protection.

POLYARYLENE SULFIDE

Without being limited thereto, uncured or partially cured poly(arylenesulfide) whether homopolymer, copolymer, terpolymer, and the like, or ablend of such polymers, can be used in the practice of the invention.The uncured or partially cured polymer is a polymer the molecular weightof which can be increased by either lengthening of a molecular chain orby crosslinking or by combination of both by supplying theretosufficient energy, such as heat. Suitable poly(arylene sulfide) polymersinclude, but are not limited to, those described in U.S. Pat. No.3,354,129, incorporated by reference herein. Examples of poly(arylenesulfide) polymers suitable for purposes of the invention includepoly(2,4-tolylene sulfide), poly(4,4'-biphenylene sulfide) andpoly(phenylene sulfide). Because of its availability and desirableproperties (such as high chemical resistance, nonflammability, and highstrength and hardness) poly(phenylene sulfide) is the presentlypreferred poly(arylene sulfide). Various poly(arylene sulfides) arecommercially available under the trademark Ryton® from PhillipsPetroleum Company, Bartlesville, Okla.

THE PRINT COMPOUNDS

The six print compounds useful in accordance with this invention toprovide laser printable polyarylene sulfide compositions arecommercially available products. The following tabulation gives asupplier and trademark for each of the print compounds.

    __________________________________________________________________________    Print Compound   Supplier    Trademark                                                                              Reference                               __________________________________________________________________________      Nickel-monoazo complex                                                                       Harmon Color Co.                                                                          Fanchon Fast                                                                           Color #12775, Pigment Green 10                                                (para                                                                Yellow Y-5694                                                                          chloroaniline → 2,4-quinoline                                           diol →                                                                nickel complex); U.S. 2,396,327           Lead chromate-lead molybdate                                                                 Dupont      Krolor KR980D                                                                          Mixture of Violet 19 and Red 104                                     (Red)    PbCrO.sub.4 /PbMoO.sub.4 ; Color                                              index number                                                                  46500 and 77605;                                                              Violet 19: U.S. 2,844,484;                                                    U.S. 2,844,485; U.S. 2,844,581                                                Red 104: U.S. 1,926,447                   Quinacridone   Sun Chemical Co.                                                                          228-0022 Violet 19; Color Index 46500                                         (Red)    Violet 19: U.S. 2,844,484;                                                    U.S. 2,844,485; U.S. 2,844,581            Nickel-antimony-titanium                                                                     Shepherd Chemical Co.                                                                     Shepherd #14                                                                           Pigment Yellow #150; made from                                       (Yellow) oxides of the metals plus heating         Cobalt-zinc-silica                                                                           Ferro Chemical Co.                                                                        V9223 (Blue)                                                                           Major components are metal oxides                                             calcined at 1200 to 2300°                                              F.                                        Lead chromate  Dupont      Krolor KY788D                                                                          PbCrO.sub.4                                                          (Yellow)                                         __________________________________________________________________________

FILLER

Various fillers can be used for the composition of this invention.Typical fillers include fiberglass, talc, titanium dioxide, silica andcalcium sulfate. Most preferably the composition of this inventioncontains one or more of the fillers fiberglass, talc and titaniumdioxide.

COUPLING AGENT

In accordance with the preferred embodiment of the invention thecomposition comprises a poly(arylene sulfide) (such as, for example, apoly(phenylene sulfide) and at least one mercaptosilane, such as, forexample, the preferred 3-mercaptopropyltrimethoxysilane. This silane ispreferred because of its extraordinary utility as a coupling agent.

OTHER ADDITIVES

The composition of this invention optionally contains other additivessuch as processing aids (e.g. mold release agents), corrosioninhibitors, and stabilizers. It is presently preferred to incorporate amold release agent into the composition of this invention, particularlywhen the composition is intended for molding, e.g. in an encapsulationoperation. Polyethylene and zinc stearate are examples of useful moldrelease agents. Corrosion inhibitors are also advantageously containedin the composition, particularly when this composition is used inmolding operations such as encapsulation. An example of a corrosioninhibitor is lithium carbonate.

PRODUCTION

The composition of this invention is preferably in the form of a powderor in the form of pellets. The ingredients are most preferably dryblended and then extruded into pellets or otherwise molten and convertedinto powder. The melting or extrusion is carried out at temperaturesabove the melting point of the polyarylene sulfide and usually at atemperature in the range of about 550° to 650° F.

LASER PRINTING

Another embodiment of this invention resides in a printing process. Inthis process a surface of a molded composition as defined above isexposed to a pattern of laser radiation such as to change the irradiatedsurface as compared to the non-irradiated surface and to generate apreferably visible mark corresponding to the pattern of irradiation onthe surface. A laser printer, Laser Mark 920, was used as described inthe example and is commercially available from Lumonics, Inc., Kanata,Canada. Generally, the pattern is generated by passing the laserradiation through a stencil. The exposure time is usually short, in theorder of microseconds and the depth of the material affected is small,usually in the order of a mil or less using a power range of the laseron the order of 1-10 joules, preferably 3 joules over an area of about0.03125 sq. inches. The specific print compounds used in thecompositions of this invention which cause laser printability with goodcontrast may involve different mechanisms such as mechanical and/orchemical changes in the composition near the surface. Applications donot wish to be bound, however, by any such theory. It should beunderstood that good contrast is a matter of interpretation and maycomprise a light pigmented resin composition which changes to dark areasunder laser exposure or vice versa. Also under varying energy levels ofthe laser the resin color may initially be changed to a lighter colorsuch as at 3 joules energy then to a darker color such as at 10 joulesenergy. The initial resin pigmentation or color (light or dark) is alsobased on pigments concentrations and resin formulations which can varyover a wide range.

ENCAPSULATION

The most preferred use of the compositions of this invention is forencapsulation of electrical elements, suchh as integrated circuits,capacitors, resistor networks, and the like. This encapsulation isachieved by flowing the composition of this invention as a melt in amold over the electric element to be encapsulated while protecting theconnecting leads from being coated. The molten composition is allowed tosolidify in the mold and then the encapsulated element is removed fromthe mold. By this process, which uses the novel composition of thisinvention, an encapsulated electrical element is produced which canreadily and readably be printed upon with laser radiation. It is withinthe scope of this invention to carry out the laser printing followingthe encapsulation and most preferably directly in the mold prior toremoval of the encapsulated element.

The encapsulation steps are generally carried out by injecting thecomposition of this invention into the mold containing the electricalelements. The temperature for this step will be preferably in the rangeof 575° to 675° F., and also based on the electrical component beingencapsulated but it will be sufficiently above the melting point of thepolyarylene sulfide to allow adequate flow of the composition into themold and around the electrical element or elements.

Although the invention is not limited thereto the viscosity of thecomposition used for encapsulation of active components should notexceed about 800 poise. Encapsulation of active electronic componentswith compositions having viscosities in excess of about 800 poise cancause damage to the components. It is contemplated that the viscosity ofthe composition will generally range from about 150 to about 500 poisefor active components other than very delicate components such as, forexample, integrated circuits with wire leads. With respect to verydelicate components such as, for example integrated circuits with wireleads the viscosity of the encapsulation composition should be belowabout 150 poise. Encapsulation of integrated circuits with compositionsany higher in viscosity can cause wire wash (i.e., breaking of the wiresof the integrated circuit). It is contemplated that the viscosity of thecomposition for the encapsulation of such integrated circuits and thelike will generally range from about 75 to about 150 poise.

Although viscosity of the composition depends on a number of factors, toobtain composition viscosities below about 800 poise the viscosity ofthe poly(arylene sulfide) contemplated in encapsulation of activecomponents should generally not exceed about 130 poise. It iscontemplated that the viscosity of the poly(arylene sulfide) will, inmost applications, range up to about 70 poise. To obtain compositionviscosities within the desired range for delicate active components suchas, for example, integrated circuits with wire leads the viscosity ofthe poly(arylene sulfide) should generally be less than about 25 poise.

Although the invention is not limited thereto the viscosity of thecomposition used for encapsulation of passive components should notexceed about 1200 poise. Encapsulation of passive electronic componentswith compositions having viscosities in excess of about 1200 poise cancause damage to the components. It is contemplated that the viscosity ofthe composition will generally range from about 500 to about 800 poise.

To obtain composition viscosities within the desired ranges theviscosity of the poly(arylene sulfide) contemplated in encapsulation ofpassive components should not exceed about 300 poise. It is contemplatedthat the viscosity of the poly(arylene sulfide) will generally rangefrom about 190 to about 300 poise.

The viscosities mentioned above are determined on a capillary rheometerat 650° F. and at a shear rate of 1000 sec⁻¹.

The following examples are intended to further illustrate the inventionwithout unduly limiting its scope.

EXAMPLE I

The ingredients of the following recipe were dry blended and thereafterthe composition was extruded in a Buss-Conduit Kneader feeding acrosshead extruder and pellets of the composition were recovered.

    ______________________________________                                                      Weight Percent                                                                          Parts by Weight                                       ______________________________________                                        Polyphenylene sulfide.sup.1                                                                   35          100                                               Fiberglass.sup.2                                                                              35          100                                               Talc.sup.3      11.75       33.6                                              Titanium dioxide.sup.4                                                                        15          42.9                                              Nickel mono-azo complex.sup.5                                                                 2           5.7                                               Silane.sup.6    1           2.9                                               Processing aid.sup.7                                                                          0.25        0.7                                               ______________________________________                                         .sup.1 Commercially available under the trademark Ryton ® from            Phillips Petroleum Company, Bartlesville, Oklahoma.                           .sup.2 Commercially available under Grade 193 from OwensCorning, Amarillo     Texas.                                                                        .sup.3 Commercially available under type 2620 talc from Ribelin, Dallas,      Texas.                                                                        .sup.4 Commercially available under the trademark Unitane 0-110 from          Cyanamid.                                                                     .sup.5 Commercially available from Harmon Chemical Co., Hawthorne, N.J.       under the trademark Harmon Y5694.                                             .sup.6 Commercially available under the trademark A189 from Union Carbide     or trademark 6032 Dow Chemical Co.                                            .sup.7 Polyethylene commercially available under the trademark Marlex         EMNTR885 from Phillips Petroleum Company, Bartlesville, Oklahoma.        

The color of the composition was golden yellow. The pellets were used toencapsulate electric circuits with satisfactory results. Laser printingof the encapsulated circuit resulted in markings having a purplish colorwith good contrast.

EXAMPLES 2-6

The ingredients of the recipe in Example I were blended in theconcentrations listed using, however, instead of the nickel monoazocomplex those compositions listed in the following table. The changes incolor due to laser energy exposure are listed.

    ______________________________________                                        Ex-              Compo-    Encap-                                             am-              sition    sulation                                                                              Resultant Laser                            ple Pigment      Color     Results Print Color                                ______________________________________                                        2   Lead chromate-                                                                             light brown                                                                             satisfactory                                                                          light yellow                                   lead molybdate                                                            3   Quinacridone dark purple                                                                             satisfactory                                                                          light green                                4   Nickel-antimony-                                                                           light tan satisfactory                                                                          light yellow                                   titanium                                                                  5   Cobalt-zinc- gray      satisfactory                                                                          white                                          silica                                                                    6   Lead chromate                                                                              gray-tan  satisfactory                                                                          light yellow                               ______________________________________                                    

All the above listed pigments showed good contrast, while a variety ofother pigments were ineffectual in exhibiting good contrast under laserenergy exposure. For example: chromium oxide (green) blended inaccordance with example 1 recipe in place of ingredient 5 and at a 1weight percent concentration when exposed to 3 joules laser energyresulted in poor contrast. The chromium oxide is commercially availablefrom Pfizer Co. under the pigment number G4099.

Reasonable variations and modifications which will become apparent tothose skilled in the art can be made in this invention without departingfrom the spirit and scope thereof.

What is claimed is:
 1. Process to encapsulate articles comprising(a)melting a composition comprising polyarylene sulfide and at least oneprint compound selected from the group consisting ofmonoazo-nickelcomplex lead chromate-lead molybdate quinacridonenickel-antimony-titanium cobalt-zinc-silica and lead chromate (b)injecting the so molten composition around the article to beencapsulated, (c) cooling the composition surrounding the article to beencapsulated, and solidifying said molten composition to form saidencapsulated article.
 2. Process in accordance with claim 1 wherein saidarticle is selected from the group consisting of electrical circuits andelements and wherein the electrical connector or connectors of saidarticle are protected from being covered with said composition.
 3. Aprocess in accordance with claim 1 comprising arranging said articleinside of an injection mold and injecting said molten composition intosaid injection mold.
 4. Process in accordance with claim 1 furthercomprising subjecting the surface of the solidified encapsulatingmaterial to a pattern of laser light irradiation such as to modify thesurface of the composition in all the areas exposed to said laser light.5. Process in accordance with claim 4 wherein said laser lightirradiation is carried out for a time sufficient to generate a patternlegible for the human eye.